Hair is a protein structure that grows from follicles found in the epidermis. The human body, apart from areas of glabrous skin, is covered in follicles which produce thick terminal and fine vellus hair. Most common interest in hair is focused on hair growth, hair types, and hair care, but hair is also an important biomaterial primarily composed of protein, known as alpha-keratin.
The word “hair” usually refers to two distinct structures:
- the part beneath the skin, called the hair follicle, or, when pulled from the skin, the bulb. This organ is located in the dermis and maintains stem cells, which not only re-grow the hair after it falls out, but also are recruited to regrow skin after a wound.
- the shaft, which is the hard filamentous part that extends above the skin surface. A cross section of the hair shaft may be divided roughly into three zones.
Hair fibers have a structure consisting of several layers, starting from the outside:
- the cuticle, which consists of several layers of flat, thin cells laid out overlapping one another as roof shingles,
- the cortex, which contains the keratin bundles in cell structures that remain roughly rod-like.
- the medulla, a disorganized and open area at the fiber’s center
Facts and Figures on Hair
- Number of hair per head: ca. 100,000
- Hair thickness (diameter): 0.06 – 0.12 mm
- Main ingredient: Keratin (thereof 10-20% Cysteine)
Hair Growth Cycle
- Formation of new cells in the hair bulb (hair matrix cells) –Known as the start of the Anagen phase.
- Duration: around 2-6 years
- Rate: around 1 cm/ month
- Keratinization of the cells above the sebaceous gland, In other words: the higher the Keratin & the Cystine , the more healthy growing hair
- Sulpha bridge: comes from Amino-Acid (Responsible for the curliness)
- 1% should be in Catagen phase.
- 10-20% should be in Telogen phase.
- The rest should be in Anagen phase.
- Normal average of hair loss per day is 100 hairs.
Hair growth is asynchronous & occurs in cycles.
Each cycle consists of 3 phases
Anagen phase = growth phase
- Hair growth due to Frequent division of hair- generating matrix cells
- Duration 2 to 6 years
Catagen phase = transition phase
- The hair-generating cells slowly stop cell division and the hair follicle shrinks and migrates towards the surface
- Duration: 2 to 3 weeks
Telogen phase = resting phase
- The hair falls out
- The hair follicle withdraws deeper into the skin and a new growth phase is beginning
- Duration: 3 to 4 months